Chapter 10 Mobile IP TCP/IP Protocol Suite

Chapter 10 Mobile IP TCP/IP Protocol Suite
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OBJECTIVES: To discuss addressing issues related to a mobile host and the need for a care-of address. To discuss two agents involved in mobile IP communication, the home agent and the foreign agent, and how they communicate. To explain three phases of communication between a mobile host and a remote host: agent discovery, registration, and data transfer. To mention inefficiency of mobile IP in two cases, double crossing and triangular routing, and a possible solution. TCP/IP Protocol Suite

Chapter Outline 10.1 Addressing 10.2 Agents 10.3 Three Phases
10.4 Inefficiency in Mobile IP TCP/IP Protocol Suite

10-1 ADDRESSING The main problem that must be solved in providing mobile communication using the IP protocol is addressing. TCP/IP Protocol Suite

Topics Discussed in the Section
Stationary Host Mobile Host TCP/IP Protocol Suite

固定主机 IP地址由两部分组成：前缀和后缀路由器利用IP地址的前缀为分组(数据报)选择路由主机移动时不能携带固定不变的IP地址
前缀是某个特定网络的地址前缀使得主机与某个网络相关联路由器利用IP地址的前缀为分组(数据报)选择路由主机移动时不能携带固定不变的IP地址 TCP/IP Protocol Suite

Note The IP addresses are designed to work with stationary hosts because part of the address defines the network to which the host is attached. TCP/IP Protocol Suite

移动主机当主机从一个网络移动到另一个网络时，IP编址结构需要修改解决方案改变地址两个地址 TCP/IP Protocol Suite

改变地址移动主机在移动到新网络时改变它的IP地址缺点：不透明(P228) TCP/IP Protocol Suite

两个地址归属地址(home address)：主机原始地址转交地址(care-of address)：外地网络临时地址
TCP/IP Protocol Suite

Figure 10.1 Home address and care-of address

mobile host moves from one network to another.
Note Mobile IP has two addresses for a mobile host: one home address and one care-of address. The home address is permanent; the care-of address changes as the mobile host moves from one network to another. TCP/IP Protocol Suite

10-2 AGENTS To make the change of address transparent to the rest of the Internet requires a home agent and a foreign agent. TCP/IP Protocol Suite

Home Agent Foreign Agent TCP/IP Protocol Suite

家乡(归属)代理移动主机家乡网络上的路由器当远程主机向移动主机发送分组时，家乡代理充当该移动主机
先由家乡代理接收分组，然后再将分组发送给处地代理 TCP/IP Protocol Suite

外地代理移动主机当前所在的外地网络路由器外地代理接收家乡代理发送过来的分组，并把分组交付给移动主机
移动主机也可充当外地代理。此时转交地址称为同址转交地址(colocated care-of address) TCP/IP Protocol Suite

Figure 10.2 Home agent and foreign agent

Note When the mobile host and the foreign agent are the same, the care-of address is called a colocated care-of address. TCP/IP Protocol Suite

10-3 THREE PHASES To communicate with a remote host, a mobile host goes through three phases: agent discovery, registration, and data transfer. The first phase, agent discovery, involves the mobile host, the foreign agent, and the home agent. The second phase, registration, also involves the mobile host and the two agents. Finally, in the third phase, the remote host is also involved. We discuss each phase separately. TCP/IP Protocol Suite

Figure 10.3 Remote host and mobile host configuration

Agent Discovery Registration Data Transfer TCP/IP Protocol Suite

代理发现发现家乡代理发现外地代理 TCP/IP Protocol Suite

代理发现报文代理通告(agent advertisement) 代理询问(agent solicitation)

代理通告在ICMP通告报文后附带代理通告 TCP/IP Protocol Suite

Note Mobile IP does not use a new packet type for agent advertisement; it uses the router advertisement packet of ICMP, and appends an agent advertisement message. TCP/IP Protocol Suite

Figure 10.4 Agent advertisement

代理询问移动主机移到外地网络，但没有收到代理通告时，发起代理询问 TCP/IP Protocol Suite

Mobile IP does not use a new packet type for agent solicitation;
Note Mobile IP does not use a new packet type for agent solicitation; it uses the router solicitation packet of ICMP. TCP/IP Protocol Suite

登记移动主机移至外地网络并发现外地代理，它必须进行登记 TCP/IP Protocol Suite

登记四个要素移动主机必须向外地代理登记移动主机必须向家乡代理登记登记截止期到了之后，移动主机必须更新登记
移动主机回到家乡网络，必须取消登记 TCP/IP Protocol Suite

登记请求移动主机将登记请求发送给外地代理，以变登记外地代理的转交地址，同时告知外地代理移动主机的家乡地址和家乡代理的地址
外地代理将登记请求转发给家乡代理家乡代理收到登记请求后就获知外地代理的地址 TCP/IP Protocol Suite

Figure 10.5 Registration request format

登记应答登记应答由家乡代理发送给外地代理，然后再转发给移动主机用于确认或拒绝登记请求 TCP/IP Protocol Suite

Figure 10.6 Registration reply format

封装登记报文被封装成UDP数据报代理使用周知端口434 移动主机使用临时端口 TCP/IP Protocol Suite

Note A registration request or reply is sent by UDP using the well-known port 434. TCP/IP Protocol Suite

数据传送(1) 从远程主机到家乡代理从家乡代理到外地代理从外地代理到移动主机从移动主机到远程主机

数据传送(2) 从远程主机到家乡代理源地址：远程主机地址目的地址：移动主机的家乡地址家乡代理代理移动主机

数据传送(3) 从家乡代理到外地代理从外地代理到移动主机从移动主机到远程主机家乡代理使用隧道技术将分组发往外地代理
外地代理将分组发给移动主机(依据转交地址) 从移动主机到远程主机源地址：移动主机家乡地址目的地址：远程主机地址在外地网络发送 TCP/IP Protocol Suite

数据传送(4) 透明性数据传送阶段，远程主机不知道移动主机的任何移动(早期方案) TCP/IP Protocol Suite

Figure Data transfer TCP/IP Protocol Suite

Note The movement of the mobile host is transparent to the rest of the Internet. TCP/IP Protocol Suite

10-4 INEFFICIENCY IN MOBILE IP
Communication involving mobile IP can be inefficient. The inefficiency can be severe or moderate. The severe case is called double crossing or 2X . The moderate case is called triangle routing or dog-leg routing. TCP/IP Protocol Suite

Double Crossing Triangle Routing Solution TCP/IP Protocol Suite

两次穿越当移动主机移至远程主机所在网络时移动主机向远程主机发送分组时，借助外地代理(远程主机所在网络的路由器)，无问题
远程主机向移动主机发送数据时，仍需要错助家乡代理进行数据传送，即发生两次穿越问题 TCP/IP Protocol Suite

Figure 10.8 Double crossing

三角路由(1) 发生三角路由问题的根源是移动主机的移动对远程主机来说是透明的解决方法
去掉透明性：远程主机同时知道移动主机的家乡地址与转交地址当家乡代理收到远程主机发给移动主机的第一个分组时，它将此分组发给外地代理，并向远程主机发送更新绑定分组(update binding packet)，让远程主机获知移动主机当前转交地址 TCP/IP Protocol Suite

Figure 10.9 Triangle routing

三角路由(2) 当移动主机与远程主机不在同一个网络时移动主机给远程主机发送分组理，无问题
远程主机给移动主机发送分组时，需要借助家乡代理，发生三角路由问题 TCP/IP Protocol Suite

Chapter 10 Mobile IP TCP/IP Protocol Suite

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